1. Field of the Invention
The present invention relates to a process for manufacture of laminated glazing units, especially those designed as equipment for vehicles of the windshield type. It relates more particularly to laminated glazing units in which the intermediate film, which is a polymer-base material disposed between rigid substrates, generally of glass, is provided with a coating having thermal properties, especially of reflection in the infrared, thus endowing these glazing units with a highly satisfactory function of protection against solar radiation.
2. Discussion of the Background
Such configurations of glazing units are known in particular from the following patents: U.S. Pat. No. 4,639,069, U.S. Pat. No. 4,369,945, EP 0303586 and WO 90/08334, wherein there are used intermediate films generally comprising a ply of transparent polymer of the polyethylene terephthalate type (PET), provided on one of its faces with the coating which reflects in the infrared, said ply being inserted between two plies of thermoplastic polymer of the polyvinyl butyral type (PVB) before the usual assembly of this multi-layer intermediate film together with the two glass substrates is performed.
A problem specific to this type of configuration soon became apparent, however: in choosing these “multi-layer intermediate films”, with dimensions identical to those of the glass plates, the infrared-reflecting coating was disposed flush with the edge wall of the glass plates. This coating usually comprises layers which are susceptible to deterioration, especially to oxidation, in contact with moisture. This is particularly true for metallic layers, especially of silver, which tend to corrode along their periphery, such corrosion progressively spreading over their entire surface and leading to optical defects and loss of thermal performances.
Suggestions toward solving this problem have already been made. For example, U.S. Pat. No. 5,131,967 describes a technique using the laser to margin the reflecting coating deposited on the PET, thus preventing it from occupying a flush position. This technique seems to be cumbersome, however, and it substantially lengthens the production time, since the laser must achieve ablation of the reflecting coating over a peripheral strip of non-negligible width.
Another suggestion was made in U.S. Pat. No. 5,320,893: this document teaches making a cut in the thickness of the PET ply, around the periphery thereof, so that the peripheral corrosion of the reflecting coating will be stopped from spreading by this break line. It is not certain that a simple line will be able to prevent all spreading of corrosion in this way.